Alkyl or alkaryl hydroxamic acids and their salts are well-known collectors for the froth flotation of oxide minerals. A study of the available published literature indicates that the term "OXIDES" is used in a generic sense and includes oxides, carbonates, phosphates, fluorides, sulfates, silicates etc. of metals, and, as such, thereby excludes sulfides, coal and metallics or metalloids. Soviet workers have found a variety of applications for such hydroxamic acids. A recent review summarizes the flotation application of alkyl hydroxamic acids (Pradip and Fuerstenau, "Mineral Flotation with Hydroxamate Collectors", in "Reagents in the Minerals Industry", Ed. M. J. Jones and R. Oblatt, Inst. Min. Met., London, 1984, pp. 161-168). Hydroxamic acids have been used for the flotation of minerals such as pyrochlore (of Nb and Ta), fluoride, huebnerite, wolframite, cassiterite, muscovite, phosphorites, hematite, pyrolusite, phodonite, chrysocolla, malachite, barite, calcite, and rare-earths all belonging to the class of "oxides". Recently its use in the beneficiation of kaolin clays was disclosed (U.S. Pat. No. 4,629,556). Novel compositions containing alkyl hydroxamates have also been disclosed recently (U.S. Pat. No. 4,929,343). Alkyl hydroxamates have also been used in conjunction with xanthates for improved recovery of oxide copper minerals. Recently the use of a hydroxamic acid was disclosed for the recovery of oxide minerals containing copper, iron, gold and silver (Zhou, Wizhi, Kuangye Gongcheng, 1985, 5-1, pp. 25-9, and iron concentrates were recovered from associated oxide minerals by flotation of Au, Ag, and Cu oxide, using a hydroxamic acid and magnetic separation for Fe. Flotation of copper oxide ores with hydroxamate and xanthate was also reported (Zhou, Weizhi, Jinshu Xuebao, 1985, 21-3, pp. B105-B111). A copper concentrate (.about.26% Cu) was obtained at 80% recovery by flotation of copper oxide ore containing malachite and pseudomalachite with hydroxamate and xanthate as collector and regulator. Silver containing gold concentrate was obtained by this method from siliceous Cu-Fe oxide ore. Alkyl hydroxamic acids or their alkali metal salts have also been used in conjunction with conventional sulfide collection such as xanthates to enhance the recovery of copper oxides from mixed sulfide-oxide ores of copper. The sulfides in these ores are typically chalcopyrites (CuFeS.sub.2), chalcocite (Cu.sub.2 S), covellite (CuS) etc. and the oxides are typically malachite (CuCO.sub.3, Cu(OH).sub.2), cuprite (Cu.sub.2 O), tenorite (CuO), and chrysocolla (CuSiO.sub.3) see U.S. Pat. No. 4,324,654.
While all of this extensive published literature certainly represents advancement of the art of flotation of oxide minerals with hydroxamates, there are still many unknowns in this art. The literature information adequately teaches that hydroxamates can float a variety of oxide minerals of many metals, yet it is not possible for those skilled in the art to predict the behavior of hydroxamates when applied to ores that are not characterized as the traditional oxides. The published literature also adequately teaches that hydroxamates are not used solely in the flotation of copper sulfide ores (for example, the prophyry or primary ore), but rather it is used in conjunction with the traditional sulfide collectors for the sole purpose of improving the recovery of oxide copper minerals which are not floated effectively by sulfide collectors. Indeed, it is not possible to predict the behavior of hydroxamates as collectors for complex ores such as the Cu-Pb-Zn-Fe, Ni-Co-Cu-Fe, Cu-Zn, Pb-Zn and massive sulfide ores. Recently alkyl hydroxamates were evaluated for the flotation beneficiation of such a complex, polymetallic ore containing nickel, copper, gold and uranium (Collee, R. Monfort, G. and Windels, F. Valorisation des minerals de cobalt Etude experimentale d'un gisement, in Annales des Mines de Belgigue, 1985, 3-4, pp. 106-131). This polymetallic deposit contained notably sulfides and arsenides (safflorite, pyrite, skutterudite, remmelsbergite, chalcopyrite, orpiments, mispickel), oxides and hydroxides (magnetitute, rutile, hematite, goethite, erythrine, pitchblende, heterogenite, brannerite), carbonates (spherocobaltite, dolmite, calcite), silicates (quartz, clay, various micas, feldspars, pyroxenes) and elements (gold, graphite). Most of the traditionally used sulfides and non-sulfide collectors were tested. The experimental reagents were notably of the following trademark types: Cataflot, Noramac, Orzan, Quebracho, Aerodepressant, AeroPromotor, Aeromine and chemicals: methylisobutylcarbinol, oleic acid, ascorbic acid, sulfides and alkaline disulfides, arkomon, amyl xanthates, ethyl xanthates, alkaline disulfides, isopropropyl ethyl thionocarbamates, sulfuric acid, sodium carbonate, sodium silicate, pine oil, terpeniol, cresol, aliphatic alcohols, sulfoesters, alkyldithiophosphates, fatty acids, petronates, sulfonates. The flotation results showed the sluggish kinetics of flotation phenomena of these ores. The operating conditions were varied to include laurohydroxamates with or without sulfuration to xanthates, variable pH, hydroxamic acid mixtures, or mixtures of their alkaline salts, mixtures of laurylamine chlorides, with or without sodium silicate and with sodium sulfhydrate. The experimental results of flotation by hydroxamate reagents were able to show the sometimes beneficial influence of these reagents, i.e. their catalyzing effect on the floatability of several cobalt oxides were predictable from the literature teachings, and one can conclude from the study that there was no unusual benefit from the use of hydroxamates per se.